Method of straightening elongated workpieces

ABSTRACT

A method of straightening long tubular or solid stock of circular, oval, square or rectangular profile according to which the stock is conveyed lengthwise, without rotation about its axis, along an elongated path having inlet and outlet ends between which the stock is flexed at a plurality of longitudinally spaced equidistant locations in directions extending transversely of a straight line connecting the inlet and outlet ends of the path. The directions of flexing, as considered in the circumferential direction of the moving stock, make an oblique angle of between 90 and 145 degrees. The flexing locations are defined by discrete passes of straightening rolls which may but need not orbit simultaneously about the aforementioned straight line.

United States Patent Fangmeier et al.

[ Mar. 26, 1974 Erich Krafft; Rolf Eckard Koch, all of Solingen, Germany [73] Assignee: Th. Kieserling & Albrecht, Solingen,

Germany [22] Filed: May 24, 1972 [21] Appl. No.: 256,584

[30] Foreign Application Priority Data May 27, 1971 Germany 2126371 [52] US. Cl. 72/162 [51] Int. Cl B2ld 3/04 [58] Field of Search 72/160, 162, 164, 78, 163

[56] References Cited UNITED STATES PATENTS 2,720,243 10/1955 Siegerist 72/162 2,084,746 6/1937 Roberts..... 72/162 2,350,274 5/1944 Duclos 72/162 299,615 6/1884 Borchardt 72/162 731,675 6/1903 Geger 72/162 3,078,909 2/1963 Maust 72/163 Primary Examiner-Milton S. Mehr Attorney, Agent, or FirmMichael S. Striker 5 7] ABSTRACT A method of straightening long tubular or solid stock of circular, oval, square or rectangular profile according to which the stock is conveyed lengthwise, without rotation about its axis, along an elongated path having inlet and outlet ends between which the stock is flexed at a plurality of longitudinally spaced equidistant locations in directions extending transversely of a straight line connecting the inlet and outlet ends of the path. The directions of flexing, as considered in the circumferential direction of the moving stock, make an oblique angle of between 90 and 145 degrees. The flexing locations are defined by discrete passes of straightening rolls which may but need not orbit simultaneously about the aforementioned straight line.

9 Claims, 8 Drawing Figures PAIENIEnums am 31798 L 948 sum 2 OF 2 METHOD OF STRAIGHTENING ELONGATED WORKPIECES BACKGROUND OF THE INVENTION The present invention relates to a method of straightening tubular or solid metallic stock, such as tubes, bars, rods or the like of circular, polygonal, oval or other cross-sectional outline. More particularly, the invention relates to improvements in a method of straightening long stock according to which the stock is held against rotation about its axis while moving lengthwise through a succession of multi-roll passes so that the bending stresses to which the stock is subjected are applied at a plurality of spaced flexing locations adjacent to the path along which the stock moves through the straightening machine.

Certain branches of the industry, particularly the reactorand boiler-making plants, often employ tubes, rods or bars of considerable length. For example, in order to reduce the number of welded joints, certain types of heat exchangers employ tubes or pipes each of which has a length in the range of 40-60 meters. As a rule, the tubular stock consists of high-quality and hence expensive material which should be processed with a minimum of waste. Therefore, such stock is produced in draw benches of substantial length or in drumtype drawing machines wherein the losses in material as a result of engagement with drawing tools are minimal. The thus obtained stock must be subjected to a straightening operation which is a time-consuming procedure, especially if the stock is very long. Furthermore, the majority of presently known straightening machines are incapable of properly treating tubular or solid stock having a length in excess of 100 feet. If such long stock can be straightened at all, the machinery must be operated at an extremely low speed which contributes significantly to the cost of the finished product.

U.S. Pat. No. 2,411,395 to Sutton discloses a round straightener with several passes of hyperboloidal rolls whose axes are inclined with reference to the pass line. This machine is designed for treatment of round stock of substantial wall thickness. Thin-walled tubes are likely to be twisted and otherwise deformed. Moreover, the rotation of long stock about its axis during travel through a straightening machine invariably presents serious problems. Thus, the trailing end of the stock will swivel, while it rotates, with a force which cannot be properly controlled when the stock is long.

It is also known to treat round or out-of-round elongated stock in a straightening machine wherein the passes of straightening rolls are mounted in a revolving frame. Reference may be had to German Pat. Nos. 1,172,518 and 1,004,018. A drawback of such straightening machines is that, due to the bulk and weight of the frame, the latter must be rotated at a relatively low speed so that the output of the machine is unsatisfactory which is particularly felt if the length of the stock exceeds 100 feet.

The publication Stahlund Eisen (Volume 8, Apr.

17, 1969, page 93) discloses a straightening machine for treatment of stock of circular or polygonal outline. The machine employs several passes of rolls which act on the stock in two different planes, namely, a first pass acts on the stock in a vertical plane and the next pass acts on the stock in a horizontal plane. Such machine exhibits the drawback that, during treatment of certain types of stock, the second pass brings about excessive deformation or bending which remains in the final product or must be remedied by a separate treatment.

Certain other types of presently known straightening machines employ several passes of rolls which are mounted in discrete holders. The holders are mounted for orbital movement along circular paths or along noncircular paths having a verticalor horizontal main axis. It was further proposed to effect orbital movements of such holders by means of two discrete drives which are mounted at right angles to and coupled with each other but operate out of phase and serve to impart to the holders a transverse movement. The stroke can be varied from zero to a predetermined maximum value. An advantage of such machines is that they can be readily converted for treatment of differently profiled stock and that they are capable of flexing the stock in different planes and to a different extent. The accuracy of treatment is satisfactory not only in connection with the straightening of round stock but also in connection with straightening of stock having a rectangular profile. During travel through the just described machine, an elongated tube, rod or bar is flexed by orbiting passes of rolls and is flexed in all directions during each revolution of a pass.

However, the just described machine also exhibits a number of serious drawbacks. Thus, the speed of lengthwise movement of the stock must be synchronized with the orbital movement of roll passes with a very high degree of accuracy. Also, the maximum permissible speed of orbital movement of roll passes is low, not only due to the mass of holders for the roll passes but also due to' the fact that the path of orbital movement of such passes is not circular. Therefore, such straightening machines (which are disclosed, for example, in German Pat. Nos. 1,205,797, 1,071,447 and 1,222,357 and in U.S. Pat. No. 2,084,746 to Roberts) failed to gain acceptance in connection with the treatment of very long stock, such as metallic pipes or rods having a length substantially exceeding 40 meters.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved method of straightening elongated stock, especially stock of substantially greater than average length, in such a way that each of a series of successive workpieces can be straightened to the same extent as the preceding workpiece and that the treatment can be completed at a speed greatly exceeding the speed of treatment in accordance with heretofore known methods.

Another object of the invention is to provide a straightening method for long stock which is equally effective in connection with treatment of solid or tubular stock as well as stock of circular, oval, polygonal or any other practical profile.

A further object of the invention is to provide a method according to which each of a series of long workpieces is of identical configuration when itleaves the straightening station irrespective of its configuration prior to treatment.

An additional object of the invention is to provide a novel and improved method of straightening metallic tubes, rods or bars having a length in excess of feet in such a way that the time required for treatment of a workpiece is but a small fraction of the time which is necessary to complete the straightening of similar stock in accordance with the presently known methods.

The method of the present invention can be resorted to for straightening of elongated solid or tubular workpieces of circular, oval, polygonal or other crosssection. It comprises the steps of conveying a workpiece lengthwise along an elongated path having longitudinally spaced inlet and outlet ends, holding the workpiece against rotation about its axis, and flexing the workpiece intermediate the inlet and outlet ends of the path at a series of successive locations and in directions extending transversely of a straight line connecting the inlet and outlet ends of the path. The directions of flexing the workpiece at successive locations of the series make an oblique angle with each other, as considered in the circumferential direction of the workpiece in the path. The angle is preferably between 90 and 145 degrees, and the locations where the workpiece is flexed between the inlet and outlet ends of the path are preferably equidistant from each other.

The flexing step may comprise subjecting the workpiece at each of the flexing locations to the action of a force acting in the respective direction and reducing the magnitude of such force from location to location so that the force acting upon the workpiece at the last location upstream of the outlet end of the path is less than necessary to flex the workpiece beyond the elastic limit of its material.

In certain instances, it is advisable to simultaneously orbit all flexing locations about a straight line connecting the inlet and outlet ends of the path. The flexing locations are defined by discrete passes of straightening rolls, and the orbiting step comprises circulating the passes about the aforementioned straight line without any appreciable changes in their orientation, i.e., the passes do not rotate about the passages which they define for successive increments of the workpiece but merely orbit about the line which connects the inlet and outlet ends of the path.

The term straightening" as used in connection with our method is intended to denote such treatment of elongated stock that each workpiece assumes a certain configuration which may but need not be that of an ideal straight tube, rod or bar. Thus, the treated workpiece may be sickle-shaped or it may resemble a corkscrew, depending on its length and on the nature of transfer mechanism which is employed to deliver workpieces to and to remove workpieces from the treating station.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved straightening method itself, however, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a transverse vertical sectional view of a workpiece having a square profile and of the directions of forces acting upon the workpiece during travel between the inlet and outlet ends of its path;

FIG. 2 is a similar view of a workpiece having a rectangular profile and of the directions of forces which act upon the workpiece atsuccessive flexing locations;

FIG. 3 is a similar view of a workpiece having a circu lar profile and of the directions of forces which act upon the workpiece during travel along its path;

FIG. 4 is a view similar to that of FIG. 3 but showing a different orientation of forces;

FIG. 5 is a similar view of still another orientation of flexing forces which act upon a workpiece of circular profile;

FIG. 6 illustrates a further distribution of forces which act upon a workpiece of circular profile;

FIG. 7 is a diagrammatic perspective view of the workpiece shown in FIG. 4 and of the flexing forces which acts upon the workpiece during travel between the inlet and outlet portions of its path; and

FIG. 8 is a perspective view of the passes of straightening rolls which act upon the workpiece of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown an elongated solid bar 1 of square cross-sectional outline. This bar is assumed to move substantially at right angles to the plane of FIG. I and is subjected to the action of eight passes of rolls which may but need not be driven. The eight passes of rolls are mounted at series of successive flexing locations between the inlet and outlet ends of the path wherein the bar I advances during treatment, and it is assumed that the neighboring passes of rolls are equidistant from each other. The first or foremost pass of rolls flexes the bar 1 in the direction a (12 oclock position) transversely of the direction of lengthwise movement of the workpiece, and more particularly at right angles to a straight line which connects the inlet and outlet ends of the path for the bar. The second pass flexes the bar I in the direction b (3 oclock position), i.e., the direction in which the bar is flexed by the first pass makes an angle of degrees with the direction of flexing by the second pass. The third pass flexes the bar 1 in the direction 0 (6 oclock position), and the fourth pass flexes the bar in the direction d (9 oclock position). The fifth, sixth, seventh and eights passes flex the bar 1 in directions respectively indicated at e,f, g and h which respectively coincide with the directions a, b, c and d. It will be noted that the directions in which the bar 1 is flexed by successive passes of straightening rolls make with each other the same oblique angle, namely, 90 degrees.

FIG. 2 illustrates the method of straightening an elongated workpiece 3 of rectangular cross-section. This workpiece is flexed by a total of eight successive passes of rolls which flex the workpiece at right angles to a straight line connecting the inlet and outlet ends of the path for the workpiece in the straightening machine. The directions in which the flexing forces act are again indicated at a to h, and it will be noted that the directions of forces acting upon the workpiece 3 at successive flexing locations between the two ends of the path make an angle of 90 degrees. The forces acting in the directions b, d, f, and h are weaker than those acting in the directions a, c, e and 3 due to the nature of profile of the workpiece. Otherwise, the workpiece 3 could undergo excessive deformation in response to application of forces acting in parallelism with its larger surfaces.

FIG. 3 illustrates the straightening of a solid rod 2 of circular profile. This rod is flexed at eight successive locations by forces acting at right angles to a straight line connecting the inlet and outlet ends of the path for the rod in the straightening machine, and the directions a to h in which successive forces act upon the rod make with each other an angle of 105 degrees, as considered in circumferential direction of the rod. FIG. 4 illustrates a similar treatment of the rod 2 in a machine having six equidistant passes of straightening rolls which flex the rod 2 in directions a tofwhereby the directions in which successive forces act make an angle of 120 degrees, as considered in the circumferential direction of the workpiece. FIG. 5 illustrates a further treatment of the rod 2 by six passes of straightening rolls acting in directions a to fwhich make an angle of 135 degrees, and FIG. 6 illustrates the treatment of a rod 2 by six passes acting in directions a to fwhich make an angle of I45 degrees, as considered in the circumferential direction of the workpiece. It is clear that FIGS. 1 to 6 illustrate only a few embodiments of the improved method because the angle between the directions of forces acting upon the workpiece at successive flexing locations can be anywhere between 90 and 145 degrees, for example, 95, 110, 130 or 140 degrees.

It will be noted that, if the angle between the directions of forces acting at successive flexing locations is relatively small, a larger number of passes is needed to complete a full 360-degree cycle. Thus, in accordance with the method of FIG. 1 or 2, the workpiece must be subjected to the action of four successive passes in order to complete a cycle whereas, in accordance with the method of FIG. 4, such cycle can be completed by resorting to only three passes. The magnitude of force which acts upon a workpiece l, 2 or 3 at the first flexing location (direction a) is preferably selected in such a way that the extent to which the workpiece is flexed exceeds the maximum bend at any point of the workpiece prior to treatment. In the treatment of square, octagonal, hexagonal, round or like stock (wherein all transverse dimensions are at least substantially equal), the magnitude of flexing forces preferably decreases from flexing location to flexing location. Thus, and referring to FIG. 1 or 3, the magnitude of the force acting in the direction b is less than that of the force acting in the direction a, the magnitude of the force acting in the direction c is less than that of the force acting in the direction b, and so forth. As a rule, the flexing of a workpiece at the last location (nearest to the outlet end of the path) is preferably such that the workpiece is flexed to below the elastic limit of its material, i.e., such flexing at the last location will result in generation of bending stresses which are preferably close to but do not actually reach the elastic limit.

The method which is illustrated in FIG. 2 can be practiced with equal advantage in connection with the straightening of stock having an oval or other crosssection wherein at least one transverse dimension greatly deviates from another transverse dimension. Otherwise stated, the method of FIG. 2 can be resorted to for straightening of stock having different moments of inertia acting in different main axes. In accordance with the method of FIG. 1, flexing of the workpiece 3 by a larger force alternates with flexing by a smaller force and vice versa.

FIG. 7 illustrates the manner in which a workpiece 2 is flexed and straightened in accordance with the method of FIG. 4. This workpiece is assumed to be a solid metallic rod of circular cross-sectional outline and is assumed to enter the straightening path at the inlet end E and leave the path at the outlet end A. The passes of straightening rolls at successive flexing locations between the inlet and outlet ends E and A are respectively indicated at I, II, III, IV, V and VI, and it will be noted that the passes are equidistant from each other. The distance between successive passes is indicated at L. The inlet end A of the path for the workpiece 2 is defined by four equidistant guide rolls 4 shown in FIG. 8, and the outlet end A of the path is defined by a group of four guide rolls 4 also shown in FIG. 8. The FIG. 8 further shows that each of the passes I to VI comprises a group of four straightening rolls 4 at least one of which may be driven to advance the workpiece 2 in the direction indicated by arrows T. The planes in which the passages between the groups of rolls 4 are located are indicated in FIG. 8 by hatching. The guide rolls 4 at the inlet end B are preceded by a first pair of auxiliary rolls 5, and the rolls 4 at the outlet end A are followed by a second pair of auxiliary rolls 6.

The straightening rolls 4 of the passes I to VI serve to support as well as to guide and flex the workpiece 2 on its way from the inlet end B toward the outlet end A. The rolls 4 at the first or foremost flexing location (nearest to the inlet end B) cause the workpiece 2 to be flexed transversely of a straight line connecting the passages defined by the rolls 4 at E and A, and such flexing takes place in the direction a and with a force which exceeds the force exerted by the rolls 4 of the pass II (direction b). The force applied by the rolls 4 of the pass III in direction a is weaker than the force acting in the direction b, and so on. As mentioned above, the force which is exerted by the rolls 4 of the pass VI is preferably slightly less than that necessary to flex the workpiece 2 to the elastic limit of its material.

FIG. 8 shows that the passages defined by rolls 4 of the passes I to VI are located at successive edges of a three-sided pyramid whereby the workpiece 2 between the passes I and II extends transversely across a first side, between II and III transversely across a second side, and between III and IV transversely across a third side of the pyramid, and so forth. The symmetry planes of the passes I to VI are normal to the longitudinal axis of the pyramid. It is evident that the flexing of workpiece 2 in FIG. 8 is greatly exaggerated for the sake of clarity. The workpiece 2 is held against rotation about its own axis and can move lengthwise in response to rotation of one or more rolls 4 or in response to exertion of a pull by the auxiliary rolls 6 or by additional transporting means located downstream of the rolls 6. The magnitude of forces to which the workpiece is subjected during travel between the inlet and outlet ends of its path depends on its cross-sectional outline (see FIG. 2), on the nature of its material, and on the initial deformation of the workpiece.

If the treatment of the workpiece 2 shown in FIGS. 7 and 8 is to be followed by treatment of a similar workpiece but consisting of a different material or having a different diameter, the basic distribution of rolls 4, 5 and 6 can remain unchanged. As a rule, the passes I to VI will be merely moved nearer to or further away from each other to either reduce or increase the distance L. However, such distance is increased uniformly between each pair of neighboring passes. The changes in distance L bring about proportional changes in the magnitude of forces acting upon the workpiece at successive flexing locations, but the directions (a to f) in which the forces act remain unchanged. Of course, if the diameter of a workpiece to be treated greatly exceeds or is considerably less than the diameter of the workpiece 2 of FIGS. 7 and 8, it might be necessary to adjust the rolls 4 of each pass to increase or reduce the crosssectional area of the passage between such rolls at the flexing locations.

It was found that the improved method allows for accurate straightening of extremely long workpieces and at a speed which is surprisingly higher than the speed at which a long workpiece can be treated in accordance with heretofore known methods. Moreover, and as shown in FIGS. 1 t 6, it has been found that the improved method can be used for straightening of long stock having any practical profile from circular to oval, from triangular to square, rectangular, pentagonal, octagonal and others. One and the same basic machine can be used for straightening of a wide variety of workpieces having different diameters and/or different lengths. It is evident, however, that the conversion of a machine from treatment of round stock to treatment of polygonal stock or vice versa might necessitate a replacement of guide rolls and straightening rolls with rolls having a different profile.

The exact details of machines which can be used for carrying out the improved method form no part of the present invention. Several types of presently known machines can be readily redesigned so as to be capable of treating long stock in a manner as described in connection with FIGS. 1 to 8. As mentioned before, one, two or all rolls of each pass can be driven and each pass is preferably adjustable lengthwise as well as transversely of a straight line connecting the inlet and outlet ends of the path for the stock. Straightening machines in which the passes are adjustable lengthwise and sideways of the workpiece are disclosed, for example, in US. Pat. No. 2,495,387 to Rummins and in German Pat. No. 100,006. The magnitude of flexing force in relation to the elastic limit of the material of a workpiece to be treated can be adjusted by moving the passes lengthwise toward or away from each other. For example, the supports for all of the passes can be telescopically connected with each other in such a way that a single reversible drive suffices to move the supports toward or away from each other whereby the distance between each pair of neighboring passes decreases or increases at the same rate. This insures that the ratio of forces acting on the workpiece at successive flexing locations remains unchanged even though the magnitude of each force changes. The distance between the adjoining passes of straightening rolis will be changed if it is desired to change the level of bending stresses in the outermost layers of treated workpieces. Thus, the adjustability of passes lengthwise of the path for a workpiece allows for highly accurate adjustment of flexing forces, for example, in order to insure that the magnitude of the force acting at the last flexing location (see the pass VI in FIG. 8) is only slightly below the elastic limit of the material of the workpiece.

As mentioned above, the workpiece which is treated in accordance with the present invention need not be exactly straight. As a rule, the treated workpiecewill resemble a crescent. Such curvature of the finished product does not interfere with storage and/or automatic lengthwise and/or sidewise transport of relatively short workpieces in a production line consisting of several machines including one or more straightening machines. if the workpieces are extremely long, e.g., about meters, they are not easy to handle ifa treated workpiece resembles a crescent or sickle. ln accordance with a feature of the invention, such very long workpieces are straightened in accordance with a slightly modified method. Since it would be impractical to treat a very long workpiece in a machine having an unusually high number of passes (as a rule, the accuracy of straightening action will depend on the number of bending forces to which the workpiece is subjected in a straightening machine), a machine for the straightening of such long workpieces preferably employs a relatively small number of passes which are mounted for orbital movement about a straight line connecting the inlet and outlet ends of the path for the workpiece. This can be readily achieved by eccentric mounting of supports for the passes of straightening rolls and by providing a common drive for all such supports. The orbital movement is preferably slow so that the centrifugal forces present no problems. Also, the orientation of rolls in each pass preferably remains unchanged, i.e., the rolls need not rotate about the respective passages for the workpiece. The just described modified method results in the making of workpieces which resemble corkscrews or helices and which, therefore, can be readily manipulated by rolling them sideways the same as a roll of coiled wire. A very long workpiece which resembles a corkscrew can be readily handled by automatic transfer mechanisms or the like to move lengthwise or sideways.

The exact adjustment of flexing forces which act upon a very long workpiece at successive flexing locations can be carried out by resorting to twin eccentrics which support and can change the positions of holders for discrete passes of straightening rolls. All such twin eccentrics can receive motion from a common shaft. As mentioned before, the conversion of a workpiece into a body resembling a corkscrew can be brought about by slowly orbiting the holders for the passes of straightening rolls about a straight line connecting the inlet and outlet ends of the path for the workpiece. Assuming that the entire system of passes completes one orbital movement in response to lengthwise movement of a workpiece through a distance of 8 meters, and if the workpiece is caused to move at a speed of 200 meters per minute, the system of passes orbits at 25 RPM which is sufficiently slow to allow for accurate and reliable control of centrifugal and other forces. By resorting to a sufficient number of passes, an extremely long workpiece can be converted into a helical or corkscrew-like body having a straight axis so that the workpiece can be rolled and otherwise manipulated in a manner which is much more convenient than the manipulation of a crescent-shaped workpiece having a length of up to and in excess of 200 feet. Referring again to the aforementioned example, the pitch of the thus obtained helical article is about 8 meters and the maximum diameter of the helix is sufficiently small to allow for convenient further processing.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and,

therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

1. A method of straightening elongated or tubular workpieces of circular or other cross-section, comprising the steps of conveying a workpiece lengthwise along an elongated path having inlet and outlet ends; holding the workpiece against rotation about its axis during lengthwise movement along said path; and flexing the workpiece intermediate said inlet and outlet ends at a series of successive locations and in directions extending transversely of a straight line connecting said inlet and outlet ends, the directions of flexing the workpiece at any two immediately successive locations of said series making oblique angles of identical magnitude of between about 90 and about ljij diees as considered in the circumferential direction of th e workpiece in said path.

2. A method as defined in claim 1, wherein said locations are equidistant from each other.

3. A method as defined in claim 1, wherein said flexing step comprises subjecting the workpiece at each of said locations to the action of a force acting in the respective direction, the magnitude of the force at each preceding location exceeding the magnitude of the force at the next-following location.

4. A method as defined in claim 1, wherein the magnitude of the force acting upon the workpiece at the last of said series of locations is less than necessary to flex the workpiece beyond the elastic limit of its material.

5. A method as defined in claim 1, further comprising the step of simultaneously orbiting said locations about said straight line.

6. A method as defined in claim 5, wherein said locations are defined by discrete passes of straightening rolls and said orbiting step comprises circulating said passes about said straight line without appreciable changes in the orientation of said rolls.

7. A method as defined in claim 1, wherein said flexing step comprises subjecting the workpiece at each of said locations to the action of a force acting in the respective direction, the forces acting upon the workpiece at successive locations of said series including alternating forces of greater and lesser magnitude.

8. A method as defined in claim 1, further comprising the step of introducing into said path a second workpiece having at least one characteristic different from that of said first mentioned workpiece, and changing the spacing between successive locations of said series prior to introduction of said second workpiece.

9. A method as defined in claim 1, wherein successive locations of said series are disposed at successive edges of a truncated pyramid. 

1. A method of straightening elongated or tubular workpieces of circular or other cross-section, comprising the steps of conveying a workpiece lengthwise along an elongated path having inlet and outlet ends; holding the workpiece against rotation about its axis during lengthwise movement along said path; and flexing the workpiece intermediate said inlet and outlet ends at a series of successive locations and in directions extending transversely of a straight line connecting said inlet and outlet ends, the directions of flexing the workpiece at any two immediately successive locations of said series making oblique angles of identical magnitude of between about 90 and about 145 degrees as considered in the circumferential direction of the workpiece in said path.
 2. A method as defined in claim 1, wherein said locations are equidistant from each other.
 3. A method as defined in claim 1, wherein said flexing step comprises subjecting the workpiece at each of said locations to the action of a force acting in the respective direction, the magnitude of the force at each preceding location exceeding the magnitude of the force at the next-following location.
 4. A method as defined in claim 1, wherein the magnitude of the force acting upon the workpiece at the last of said series of locations is less than necessary to flex the workpiece beyond the elastic limit of its material.
 5. A method as defined in claim 1, further comprising the step of simultaneously orbiting said locations about said straight line.
 6. A method as defined in claim 5, wherein said locations are defined by discrete passes of straightening rolls and said orbiting step comprises circulating said passes about said straight line without appreciable changes in the orientation of said rolls.
 7. A method as defined in claim 1, wherein said flexing step comprises subjecting the workpiece at each of said locations to the action of a force acting In the respective direction, the forces acting upon the workpiece at successive locations of said series including alternating forces of greater and lesser magnitude.
 8. A method as defined in claim 1, further comprising the step of introducing into said path a second workpiece having at least one characteristic different from that of said first mentioned workpiece, and changing the spacing between successive locations of said series prior to introduction of said second workpiece.
 9. A method as defined in claim 1, wherein successive locations of said series are disposed at successive edges of a truncated pyramid. 